﻿//
// gif.h
// by Charlie Tangora
// Public domain.
// Email me : ctangora -at- gmail -dot- com
//
// This file offers a simple, very limited way to create animated GIFs directly in code.
//
// Those looking for particular cleverness are likely to be disappointed; it's pretty
// much a straight-ahead implementation of the GIF format with optional Floyd-Steinberg
// dithering. (It does at least use delta encoding - only the changed portions of each
// frame are saved.)
//
// So resulting files are often quite large. The hope is that it will be handy nonetheless
// as a quick and easily-integrated way for programs to spit out animations.
//
// Only RGBA8 is currently supported as an input format. (The alpha is ignored.)
//
// USAGE:
// Create a GifWriter struct. Pass it to GifBegin() to initialize and write the header.
// Pass subsequent frames to GifWriteFrame().
// Finally, call GifEnd() to close the file handle and free memory.
//

#ifndef __gif_h__
#define __gif_h__

#include <stdio.h>   // for FILE*
#include <string.h>  // for memcpy and bzero
#include <stdint.h>  // for integer typedefs

// Define these macros to hook into a custom memory allocator.
// TEMP_MALLOC and TEMP_FREE will only be called in stack fashion - frees in the reverse order of mallocs
// and any temp memory allocated by a function will be freed before it exits.
// MALLOC and FREE are used only by GifBegin and GifEnd respectively (to allocate a buffer the size of the image, which
// is used to find changed pixels for delta-encoding.)

#ifndef GIF_TEMP_MALLOC
#include <stdlib.h>
#define GIF_TEMP_MALLOC malloc
#endif

#ifndef GIF_TEMP_FREE
#include <stdlib.h>
#define GIF_TEMP_FREE free
#endif

#ifndef GIF_MALLOC
#include <stdlib.h>
#define GIF_MALLOC malloc
#endif

#ifndef GIF_FREE
#include <stdlib.h>
#define GIF_FREE free
#endif

class Gif
{
public:
    int kGifTransIndex;
    struct GifPalette {
        int bitDepth;
        uint8_t r[256];
        uint8_t g[256];
        uint8_t b[256];
        // k-d tree over RGB space, organized in heap fashion
        // i.e. left child of node i is node i*2, right child is node i*2+1
        // nodes 256-511 are implicitly the leaves, containing a color
        uint8_t treeSplitElt[255];
        uint8_t treeSplit[255];
    };

    // max, min, and abs functions
    int GifIMax(int l, int r)
    {
        return l > r ? l : r;
    }
    int GifIMin(int l, int r)
    {
        return l < r ? l : r;
    }
    int GifIAbs(int i)
    {
        return i < 0 ? -i : i;
    }

    // walks the k-d tree to pick the palette entry for a desired color.
    // Takes as in/out parameters the current best color and its error -
    // only changes them if it finds a better color in its subtree.
    // this is the major hotspot in the code at the moment.
    void GifGetClosestPaletteColor(GifPalette *pPal, int r, int g, int b, int &bestInd, int &bestDiff, int treeRoot = 1)
    {
        // base case, reached the bottom of the tree
        if(treeRoot > (1 << pPal->bitDepth) - 1) {
            int ind = treeRoot - (1 << pPal->bitDepth);
            if(ind == kGifTransIndex) {
                return;
            }
            // check whether this color is better than the current winner
            int r_err = r - ((int32_t)pPal->r[ind]);
            int g_err = g - ((int32_t)pPal->g[ind]);
            int b_err = b - ((int32_t)pPal->b[ind]);
            int diff = GifIAbs(r_err) + GifIAbs(g_err) + GifIAbs(b_err);
            if(diff < bestDiff) {
                bestInd = ind;
                bestDiff = diff;
            }
            return;
        }
        // take the appropriate color (r, g, or b) for this node of the k-d tree
        int comps[3];
        comps[0] = r;
        comps[1] = g;
        comps[2] = b;
        int splitComp = comps[pPal->treeSplitElt[treeRoot]];

        int splitPos = pPal->treeSplit[treeRoot];
        if(splitPos > splitComp) {
            // check the left subtree
            GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot * 2);
            if( bestDiff > splitPos - splitComp ) {
                // cannot prove there's not a better value in the right subtree, check that too
                GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot * 2 + 1);
            }
        } else {
            GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot * 2 + 1);
            if( bestDiff > splitComp - splitPos ) {
                GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot * 2);
            }
        }
    }

    void GifSwapPixels(uint8_t *image, int pixA, int pixB)
    {
        uint8_t rA = image[pixA * 4];
        uint8_t gA = image[pixA * 4 + 1];
        uint8_t bA = image[pixA * 4 + 2];
        uint8_t aA = image[pixA * 4 + 3];

        uint8_t rB = image[pixB * 4];
        uint8_t gB = image[pixB * 4 + 1];
        uint8_t bB = image[pixB * 4 + 2];
        uint8_t aB = image[pixA * 4 + 3];

        image[pixA * 4] = rB;
        image[pixA * 4 + 1] = gB;
        image[pixA * 4 + 2] = bB;
        image[pixA * 4 + 3] = aB;

        image[pixB * 4] = rA;
        image[pixB * 4 + 1] = gA;
        image[pixB * 4 + 2] = bA;
        image[pixB * 4 + 3] = aA;
    }

    // just the partition operation from quicksort
    int GifPartition(uint8_t *image, const int left, const int right, const int elt, int pivotIndex)
    {
        const int pivotValue = image[(pivotIndex) * 4 + elt];
        GifSwapPixels(image, pivotIndex, right - 1);
        int storeIndex = left;
        bool split = 0;
        for(int ii = left; ii < right - 1; ++ii) {
            int arrayVal = image[ii * 4 + elt];
            if( arrayVal < pivotValue ) {
                GifSwapPixels(image, ii, storeIndex);
                ++storeIndex;
            } else if( arrayVal == pivotValue ) {
                if(split) {
                    GifSwapPixels(image, ii, storeIndex);
                    ++storeIndex;
                }
                split = !split;
            }
        }
        GifSwapPixels(image, storeIndex, right - 1);
        return storeIndex;
    }

    // Perform an incomplete sort, finding all elements above and below the desired median
    void GifPartitionByMedian(uint8_t *image, int left, int right, int com, int neededCenter)
    {
        if (left < right - 1) {
            int pivotIndex = left + (right - left) / 2;
            pivotIndex = GifPartition(image, left, right, com, pivotIndex);
            // Only "sort" the section of the array that contains the median
            if(pivotIndex > neededCenter) {
                GifPartitionByMedian(image, left, pivotIndex, com, neededCenter);
            }
            if(pivotIndex < neededCenter) {
                GifPartitionByMedian(image, pivotIndex + 1, right, com, neededCenter);
            }
        }
    }

    // Builds a palette by creating a balanced k-d tree of all pixels in the image
    void GifSplitPalette(uint8_t *image,
                         int numPixels, int firstElt,
                         int lastElt, int splitElt,
                         int splitDist, int treeNode,
                         bool buildForDither, GifPalette *pal)
    {
        if (lastElt <= firstElt || numPixels == 0) {
            return;
        }
        // base case, bottom of the tree
        if (lastElt == firstElt + 1) {
            if (buildForDither) {
                // Dithering needs at least one color as dark as anything
                // in the image and at least one brightest color -
                // otherwise it builds up error and produces strange artifacts
                if( firstElt == 1 ) {
                    // special case: the darkest color in the image
                    uint32_t r = 255, g = 255, b = 255;
                    for(int ii = 0; ii < numPixels; ++ii) {
                        r = (uint32_t)GifIMin((int32_t)r, image[ii * 4 + 0]);
                        g = (uint32_t)GifIMin((int32_t)g, image[ii * 4 + 1]);
                        b = (uint32_t)GifIMin((int32_t)b, image[ii * 4 + 2]);
                    }
                    pal->r[firstElt] = (uint8_t)r;
                    pal->g[firstElt] = (uint8_t)g;
                    pal->b[firstElt] = (uint8_t)b;
                    return;
                }

                if ( firstElt == (1 << pal->bitDepth) - 1 ) {
                    // special case: the lightest color in the image
                    uint32_t r = 0, g = 0, b = 0;
                    for(int ii = 0; ii < numPixels; ++ii) {
                        r = (uint32_t)GifIMax((int32_t)r, image[ii * 4 + 0]);
                        g = (uint32_t)GifIMax((int32_t)g, image[ii * 4 + 1]);
                        b = (uint32_t)GifIMax((int32_t)b, image[ii * 4 + 2]);
                    }
                    pal->r[firstElt] = (uint8_t)r;
                    pal->g[firstElt] = (uint8_t)g;
                    pal->b[firstElt] = (uint8_t)b;
                    return;
                }
            }
            // otherwise, take the average of all colors in this subcube
            uint64_t r = 0, g = 0, b = 0;
            for (int ii = 0; ii < numPixels; ++ii) {
                r += image[ii * 4 + 0];
                g += image[ii * 4 + 1];
                b += image[ii * 4 + 2];
            }

            r += (uint64_t)numPixels / 2;  // round to nearest
            g += (uint64_t)numPixels / 2;
            b += (uint64_t)numPixels / 2;

            r /= (uint64_t)numPixels;
            g /= (uint64_t)numPixels;
            b /= (uint64_t)numPixels;

            pal->r[firstElt] = (uint8_t)r;
            pal->g[firstElt] = (uint8_t)g;
            pal->b[firstElt] = (uint8_t)b;
            return;
        }
        // Find the axis with the largest range
        int minR = 255, maxR = 0;
        int minG = 255, maxG = 0;
        int minB = 255, maxB = 0;
        for(int ii = 0; ii < numPixels; ++ii) {
            int r = image[ii * 4 + 0];
            int g = image[ii * 4 + 1];
            int b = image[ii * 4 + 2];

            if(r > maxR) {
                maxR = r;
            }
            if(r < minR) {
                minR = r;
            }

            if(g > maxG) {
                maxG = g;
            }
            if(g < minG) {
                minG = g;
            }

            if(b > maxB) {
                maxB = b;
            }
            if(b < minB) {
                minB = b;
            }
        }

        int rRange = maxR - minR;
        int gRange = maxG - minG;
        int bRange = maxB - minB;
        // and split along that axis. (incidentally, this means this isn't a "proper" k-d tree but I don't know what else to call it)
        int splitCom = 1;
        if (bRange > gRange) {
            splitCom = 2;
        }
        if (rRange > bRange && rRange > gRange) {
            splitCom = 0;
        }

        int subPixelsA = numPixels * (splitElt - firstElt) / (lastElt - firstElt);
        int subPixelsB = numPixels - subPixelsA;

        GifPartitionByMedian(image, 0, numPixels, splitCom, subPixelsA);

        pal->treeSplitElt[treeNode] = (uint8_t)splitCom;
        pal->treeSplit[treeNode] = image[subPixelsA * 4 + splitCom];

        GifSplitPalette(image,              subPixelsA, firstElt, splitElt, splitElt - splitDist, splitDist / 2, treeNode * 2,   buildForDither, pal);
        GifSplitPalette(image + subPixelsA * 4, subPixelsB, splitElt, lastElt,  splitElt + splitDist, splitDist / 2, treeNode * 2 + 1, buildForDither, pal);
    }

    // Finds all pixels that have changed from the previous image and
    // moves them to the fromt of th buffer.
    // This allows us to build a palette optimized for the colors of the
    // changed pixels only.
    int GifPickChangedPixels( const uint8_t *lastFrame, uint8_t *frame, int numPixels )
    {
        int numChanged = 0;
        uint8_t *writeIter = frame;
        for (int ii = 0; ii < numPixels; ++ii) {
            if(lastFrame[0] != frame[0] ||
                    lastFrame[1] != frame[1] ||
                    lastFrame[2] != frame[2]) {
                writeIter[0] = frame[0];
                writeIter[1] = frame[1];
                writeIter[2] = frame[2];
                ++numChanged;
                writeIter += 4;
            }
            lastFrame += 4;
            frame += 4;
        }
        return numChanged;
    }

    // Creates a palette by placing all the image pixels in a k-d tree and then averaging the blocks at the bottom.
    // This is known as the "modified median split" technique
    void GifMakePalette( const uint8_t *lastFrame,
                         const uint8_t *nextFrame,
                         uint32_t width, uint32_t height,
                         int bitDepth, bool buildForDither,
                         GifPalette *pPal )
    {
        pPal->bitDepth = bitDepth;

        // SplitPalette is destructive (it sorts the pixels by color) so
        // we must create a copy of the image for it to destroy
        size_t imageSize = (size_t)(width * height * 4 * sizeof(uint8_t));
        uint8_t *destroyableImage = (uint8_t *)GIF_TEMP_MALLOC(imageSize);
        memcpy(destroyableImage, nextFrame, imageSize);

        int numPixels = (int)(width * height);
        if(lastFrame) {
            numPixels = GifPickChangedPixels(lastFrame, destroyableImage, numPixels);
        }

        const int lastElt = 1 << bitDepth;
        const int splitElt = lastElt / 2;
        const int splitDist = splitElt / 2;

        GifSplitPalette(destroyableImage, numPixels, 1, lastElt, splitElt, splitDist, 1, buildForDither, pPal);

        GIF_TEMP_FREE(destroyableImage);

        // add the bottom node for the transparency index
        pPal->treeSplit[1 << (bitDepth - 1)] = 0;
        pPal->treeSplitElt[1 << (bitDepth - 1)] = 0;

        pPal->r[0] = pPal->g[0] = pPal->b[0] = 0;
    }

    // Implements Floyd-Steinberg dithering, writes palette value to alpha
    void GifDitherImage( const uint8_t *lastFrame, const uint8_t *nextFrame,
                         uint8_t *outFrame, uint32_t width,
                         uint32_t height, GifPalette *pPal )
    {
        int numPixels = (int)(width * height);

        // quantPixels initially holds color*256 for all pixels
        // The extra 8 bits of precision allow for sub-single-color error values
        // to be propagated
        int32_t *quantPixels = (int32_t *)GIF_TEMP_MALLOC(sizeof(int32_t) * (size_t)numPixels * 4);
        for( int ii = 0; ii < numPixels * 4; ++ii ) {
            uint8_t pix = nextFrame[ii];
            int32_t pix16 = int32_t(pix) * 256;
            quantPixels[ii] = pix16;
        }

        for( uint32_t yy = 0; yy < height; ++yy ) {
            for( uint32_t xx = 0; xx < width; ++xx ) {
                int32_t *nextPix = quantPixels + 4 * (yy * width + xx);
                const uint8_t *lastPix = lastFrame ? lastFrame + 4 * (yy * width + xx) : NULL;
                // Compute the colors we want (rounding to nearest)
                int32_t rr = (nextPix[0] + 127) / 256;
                int32_t gg = (nextPix[1] + 127) / 256;
                int32_t bb = (nextPix[2] + 127) / 256;
                // if it happens that we want the color from last frame, then just write out
                // a transparent pixel
                if( lastFrame &&
                        lastPix[0] == rr &&
                        lastPix[1] == gg &&
                        lastPix[2] == bb ) {
                    nextPix[0] = rr;
                    nextPix[1] = gg;
                    nextPix[2] = bb;
                    nextPix[3] = kGifTransIndex;
                    continue;
                }

                int32_t bestDiff = 1000000;
                int32_t bestInd = kGifTransIndex;
                // Search the palete
                GifGetClosestPaletteColor(pPal, rr, gg, bb, bestInd, bestDiff);
                // Write the result to the temp buffer
                int32_t r_err = nextPix[0] - int32_t(pPal->r[bestInd]) * 256;
                int32_t g_err = nextPix[1] - int32_t(pPal->g[bestInd]) * 256;
                int32_t b_err = nextPix[2] - int32_t(pPal->b[bestInd]) * 256;

                nextPix[0] = pPal->r[bestInd];
                nextPix[1] = pPal->g[bestInd];
                nextPix[2] = pPal->b[bestInd];
                nextPix[3] = bestInd;

                // Propagate the error to the four adjacent locations
                // that we haven't touched yet
                int quantloc_7 = (int)(yy * width + xx + 1);
                int quantloc_3 = (int)(yy * width + width + xx - 1);
                int quantloc_5 = (int)(yy * width + width + xx);
                int quantloc_1 = (int)(yy * width + width + xx + 1);

                if(quantloc_7 < numPixels) {
                    int32_t *pix7 = quantPixels + 4 * quantloc_7;
                    pix7[0] += GifIMax( -pix7[0], r_err * 7 / 16 );
                    pix7[1] += GifIMax( -pix7[1], g_err * 7 / 16 );
                    pix7[2] += GifIMax( -pix7[2], b_err * 7 / 16 );
                }

                if(quantloc_3 < numPixels) {
                    int32_t *pix3 = quantPixels + 4 * quantloc_3;
                    pix3[0] += GifIMax( -pix3[0], r_err * 3 / 16 );
                    pix3[1] += GifIMax( -pix3[1], g_err * 3 / 16 );
                    pix3[2] += GifIMax( -pix3[2], b_err * 3 / 16 );
                }

                if(quantloc_5 < numPixels) {
                    int32_t *pix5 = quantPixels + 4 * quantloc_5;
                    pix5[0] += GifIMax( -pix5[0], r_err * 5 / 16 );
                    pix5[1] += GifIMax( -pix5[1], g_err * 5 / 16 );
                    pix5[2] += GifIMax( -pix5[2], b_err * 5 / 16 );
                }

                if(quantloc_1 < numPixels) {
                    int32_t *pix1 = quantPixels + 4 * quantloc_1;
                    pix1[0] += GifIMax( -pix1[0], r_err / 16 );
                    pix1[1] += GifIMax( -pix1[1], g_err / 16 );
                    pix1[2] += GifIMax( -pix1[2], b_err / 16 );
                }
            }
        }
        // Copy the palettized result to the output buffer
        for( int ii = 0; ii < numPixels * 4; ++ii ) {
            outFrame[ii] = (uint8_t)quantPixels[ii];
        }

        GIF_TEMP_FREE(quantPixels);
    }

    // Picks palette colors for the image using simple thresholding, no dithering
    void GifThresholdImage( const uint8_t *lastFrame, const uint8_t *nextFrame,
                            uint8_t *outFrame, uint32_t width, uint32_t height,
                            GifPalette *pPal )
    {
        uint32_t numPixels = width * height;
        for( uint32_t ii = 0; ii < numPixels; ++ii ) {
            // if a previous color is available, and it matches the current color,
            // set the pixel to transparent
            if(lastFrame &&
                    lastFrame[0] == nextFrame[0] &&
                    lastFrame[1] == nextFrame[1] &&
                    lastFrame[2] == nextFrame[2]) {
                outFrame[0] = lastFrame[0];
                outFrame[1] = lastFrame[1];
                outFrame[2] = lastFrame[2];
                outFrame[3] = kGifTransIndex;
            } else {
                // palettize the pixel
                int32_t bestDiff = 1000000;
                int32_t bestInd = 1;
                GifGetClosestPaletteColor(pPal, nextFrame[0], nextFrame[1], nextFrame[2], bestInd, bestDiff);

                // Write the resulting color to the output buffer
                outFrame[0] = pPal->r[bestInd];
                outFrame[1] = pPal->g[bestInd];
                outFrame[2] = pPal->b[bestInd];
                outFrame[3] = (uint8_t)bestInd;
            }
            if(lastFrame) {
                lastFrame += 4;
            }
            outFrame += 4;
            nextFrame += 4;
        }
    }

    // Simple structure to write out the LZW-compressed portion of the image
    // one bit at a time
    struct GifBitStatus {
        uint8_t bitIndex;  // how many bits in the partial byte written so far
        uint8_t byte;      // current partial byte

        uint32_t chunkIndex;
        uint8_t chunk[256];   // bytes are written in here until we have 256 of them, then written to the file
    };

    // insert a single bit
    void GifWriteBit( GifBitStatus &stat, uint32_t bit )
    {
        bit = bit & 1;
        bit = bit << stat.bitIndex;
        stat.byte |= bit;

        ++stat.bitIndex;
        if( stat.bitIndex > 7 ) {
            // move the newly-finished byte to the chunk buffer
            stat.chunk[stat.chunkIndex++] = stat.byte;
            // and start a new byte
            stat.bitIndex = 0;
            stat.byte = 0;
        }
    }

    // write all bytes so far to the file
    void GifWriteChunk( FILE *f, GifBitStatus &stat )
    {
        fputc((int)stat.chunkIndex, f);
        fwrite(stat.chunk, 1, stat.chunkIndex, f);

        stat.bitIndex = 0;
        stat.byte = 0;
        stat.chunkIndex = 0;
    }

    void GifWriteCode( FILE *f, GifBitStatus &stat, uint32_t code, uint32_t length )
    {
        for( uint32_t ii = 0; ii < length; ++ii ) {
            GifWriteBit(stat, code);
            code = code >> 1;
            if( stat.chunkIndex == 255 ) {
                GifWriteChunk(f, stat);
            }
        }
    }

    // The LZW dictionary is a 256-ary tree constructed as the file is encoded,
    // this is one node
    struct GifLzwNode {
        uint16_t m_next[256];
    };

    // write a 256-color (8-bit) image palette to the file
    void GifWritePalette( const GifPalette *pPal, FILE *f )
    {
        fputc(0, f);  // first color: transparency
        fputc(0, f);
        fputc(0, f);
        for(int ii = 1; ii < (1 << pPal->bitDepth); ++ii) {
            uint32_t r = pPal->r[ii];
            uint32_t g = pPal->g[ii];
            uint32_t b = pPal->b[ii];
            fputc((int)r, f);
            fputc((int)g, f);
            fputc((int)b, f);
        }
    }

    // write the image header, LZW-compress and write out the image
    void GifWriteLzwImage(FILE *f, uint8_t *image, uint32_t left,
                          uint32_t top,  uint32_t width,
                          uint32_t height, uint32_t delay,
                          GifPalette *pPal)
    {
        // graphics control extension
        fputc(0x21, f);
        fputc(0xf9, f);
        fputc(0x04, f);
        fputc(0x05, f); // leave prev frame in place, this frame has transparency
        fputc(delay & 0xff, f);
        fputc((delay >> 8) & 0xff, f);
        fputc(kGifTransIndex, f); // transparent color index
        fputc(0, f);

        fputc(0x2c, f); // image descriptor block

        fputc(left & 0xff, f);           // corner of image in canvas space
        fputc((left >> 8) & 0xff, f);
        fputc(top & 0xff, f);
        fputc((top >> 8) & 0xff, f);

        fputc(width & 0xff, f);          // width and height of image
        fputc((width >> 8) & 0xff, f);
        fputc(height & 0xff, f);
        fputc((height >> 8) & 0xff, f);

        //fputc(0, f); // no local color table, no transparency
        //fputc(0x80, f); // no local color table, but transparency

        fputc(0x80 + pPal->bitDepth - 1, f); // local color table present, 2 ^ bitDepth entries
        GifWritePalette(pPal, f);

        const int minCodeSize = pPal->bitDepth;
        const uint32_t clearCode = 1 << pPal->bitDepth;

        fputc(minCodeSize, f); // min code size 8 bits

        GifLzwNode *codetree = (GifLzwNode *)GIF_TEMP_MALLOC(sizeof(GifLzwNode) * 4096);

        memset(codetree, 0, sizeof(GifLzwNode) * 4096);
        int32_t curCode = -1;
        uint32_t codeSize = (uint32_t)minCodeSize + 1;
        uint32_t maxCode = clearCode + 1;

        GifBitStatus stat;
        stat.byte = 0;
        stat.bitIndex = 0;
        stat.chunkIndex = 0;

        GifWriteCode(f, stat, clearCode, codeSize);  // start with a fresh LZW dictionary

        for(uint32_t yy = 0; yy < height; ++yy) {
            for(uint32_t xx = 0; xx < width; ++xx) {
                uint8_t nextValue = image[(yy * width + xx) * 4 + 3];
                // "loser mode" - no compression, every single code is followed immediately by a clear
                //WriteCode( f, stat, nextValue, codeSize );
                //WriteCode( f, stat, 256, codeSize );
                if( curCode < 0 ) {
                    // first value in a new run
                    curCode = nextValue;
                } else if( codetree[curCode].m_next[nextValue] ) {
                    // current run already in the dictionary
                    curCode = codetree[curCode].m_next[nextValue];
                } else {
                    // finish the current run, write a code
                    GifWriteCode(f, stat, (uint32_t)curCode, codeSize);
                    // insert the new run into the dictionary
                    codetree[curCode].m_next[nextValue] = (uint16_t)++maxCode;
                    if( maxCode >= (1ul << codeSize) ) {
                        // dictionary entry count has broken a size barrier,
                        // we need more bits for codes
                        codeSize++;
                    }
                    if( maxCode == 4095 ) {
                        // the dictionary is full, clear it out and begin anew
                        GifWriteCode(f, stat, clearCode, codeSize); // clear tree

                        memset(codetree, 0, sizeof(GifLzwNode) * 4096);
                        codeSize = (uint32_t)(minCodeSize + 1);
                        maxCode = clearCode + 1;
                    }
                    curCode = nextValue;
                }
            }
        }
        // compression footer
        GifWriteCode(f, stat, (uint32_t)curCode, codeSize);
        GifWriteCode(f, stat, clearCode, codeSize);
        GifWriteCode(f, stat, clearCode + 1, (uint32_t)minCodeSize + 1);
        // write out the last partial chunk
        while( stat.bitIndex ) {
            GifWriteBit(stat, 0);
        }
        if( stat.chunkIndex ) {
            GifWriteChunk(f, stat);
        }

        fputc(0, f); // image block terminator

        GIF_TEMP_FREE(codetree);
    }

    struct GifWriter {
        FILE *f;
        uint8_t *oldImage;
        bool firstFrame;
    };

    // Creates a gif file.
    // The input GIFWriter is assumed to be uninitialized.
    // The delay value is the time between frames in hundredths of a second - note that not all viewers pay much attention to this value.
    bool GifBegin( GifWriter *writer, const char *filename,
                   uint32_t width, uint32_t height,
                   uint32_t delay, int32_t bitDepth = 8,
                   bool dither = false )
    {
        (void)bitDepth;
        (void)dither; // Mute "Unused argument" warnings
#if defined(_MSC_VER) && (_MSC_VER >= 1400)
        writer->f = 0;
        fopen_s(&writer->f, filename, "wb");
#else
        writer->f = fopen(filename, "wb");
#endif
        if(!writer->f) {
            return false;
        }

        writer->firstFrame = true;

        // allocate
        writer->oldImage = (uint8_t *)GIF_MALLOC(width * height * 4);
        fputs("GIF89a", writer->f);

        // screen descriptor
        fputc(width & 0xff, writer->f);
        fputc((width >> 8) & 0xff, writer->f);
        fputc(height & 0xff, writer->f);
        fputc((height >> 8) & 0xff, writer->f);

        fputc(0xf0, writer->f);  // there is an unsorted global color table of 2 entries
        fputc(0, writer->f);     // background color
        fputc(0, writer->f);     // pixels are square (we need to specify this because it's 1989)

        // now the "global" palette (really just a dummy palette)
        // color 0: black
        fputc(0, writer->f);
        fputc(0, writer->f);
        fputc(0, writer->f);
        // color 1: also black
        fputc(0, writer->f);
        fputc(0, writer->f);
        fputc(0, writer->f);

        if( delay != 0 ) {
            // animation header
            fputc(0x21, writer->f); // extension
            fputc(0xff, writer->f); // application specific
            fputc(11, writer->f); // length 11
            fputs("NETSCAPE2.0", writer->f); // yes, really
            fputc(3, writer->f); // 3 bytes of NETSCAPE2.0 data

            fputc(1, writer->f); // JUST BECAUSE
            fputc(0, writer->f); // loop infinitely (byte 0)
            fputc(0, writer->f); // loop infinitely (byte 1)

            fputc(0, writer->f); // block terminator
        }
        return true;
    }

    // Writes out a new frame to a GIF in progress.
    // The GIFWriter should have been created by GIFBegin.
    // AFAIK, it is legal to use different bit depths for different frames of an image -
    // this may be handy to save bits in animations that don't change much.
    bool GifWriteFrame( GifWriter *writer, const uint8_t *image,
                        uint32_t width, uint32_t height,
                        uint32_t delay, int bitDepth = 8, bool dither = false )
    {
        if(!writer->f) {
            return false;
        }

        const uint8_t *oldImage = writer->firstFrame ? NULL : writer->oldImage;
        writer->firstFrame = false;

        GifPalette pal;
        GifMakePalette((dither ? NULL : oldImage), image, width, height, bitDepth, dither, &pal);

        if(dither) {
            GifDitherImage(oldImage, image, writer->oldImage, width, height, &pal);
        } else {
            GifThresholdImage(oldImage, image, writer->oldImage, width, height, &pal);
        }

        GifWriteLzwImage(writer->f, writer->oldImage, 0, 0, width, height, delay, &pal);

        return true;
    }

    // Writes the EOF code, closes the file handle, and frees temp memory used by a GIF.
    // Many if not most viewers will still display a GIF properly if the EOF code is missing,
    // but it's still a good idea to write it out.
    bool GifEnd( GifWriter *writer )
    {
        if(!writer->f) {
            return false;
        }

        fputc(0x3b, writer->f); // end of file
        fclose(writer->f);
        GIF_FREE(writer->oldImage);

        writer->f = NULL;
        writer->oldImage = NULL;

        return true;
    }
};

#endif
